I'm against a disposable cartridge type prefilter for a softener because human nature being what it is, many guys won't change the cartridge until they can't power wash their butt in the shower and by then it is way past the time it should have been changed and it has starved the softener for proper backwash water flow which has been harming the resin. That is not good for a softener.
I think you meant to say that chlorine harms resin instead of resin explodes... and yes chlorine over time harms resin but, it takes many years to notice it. And if you remove it at the softener, the softener and the whole house is unprotected from bacteria in the city water system. Relatively speaking, resin is much less expensive than many years of replacing carbon cartridges.